Fast fault current interruption on high-power DC networks

This paper investigates methods for DC fault current interruption in high-power DC networks. It is shown that mechanical DC circuit breakers could only offer adequate protection if supplemented with fault current limiters. A simple electronic switch (IGBT or GTO) is suitable as a DC circuit breaker but the component sizing crucially depends on the speed of signal processing circuits. It is likely that significant component overrating will be required. The simple DC/DC converters are studied as DC circuit breakers and it is found that they offer some important advantages over series electronic switches. However DC/DC converters can not provide fault current interruption for all fault cases. A resonant high-power DC/DC converter is studied under extreme fault conditions. It is shown that the converter operates uninterrupted through most severe faults, and inherent stabilising properties prevent any overvoltage or extreme currents. The converter experiences overcurrents on faulted terminals at levels that can be tolerated by the thyristors. The detailed simulations demonstrate that the converter is capable of responding like an open circuit on unfaulted terminals. The impact of unbalanced DC line faults on a bipolar DC system is also discussed.